3G Micro cell upgrade.

A  4g Micro cell would have no purpose. It is a voice device and has no need for additional speed.

@rjniles - nice to see you back 

I haven't been away. I visit about once a week. Just haven't seen any posts I can or care to add any value to.

Yeah, I know the feeling, but I'm kinda obligated 

Why are you using a micro cell for data when you have an internet connection?

The microcell isn't my turf, but the difference between 3G and 4G I can comment on.

ATT carries voice over GSM, Edge or HSPA/hspa+.   Hspa+ is often called 4G and speed tests are more like 3.5 - 3.75 G 

HD voice, or VoLTE is the latest tech, and many newer smartphones are HD voice capable.  

You can read more than you ever wanted to know about the different technology here. 

http://www.4gltemall.com/blog/what-is-gsm-edge-gprs-umts-3g-hsdpa-hsupa-lte/

I have marginal service at home.  The Nexus 6p got great reception, iPhone 5s lousy reception, I have had several Samsung phones with varied results.  Wifi calling on GS6 and GS7 was fair to fantastic, depending on which update made it so (grrrrrr).  

Best so far ....Google Pixel.   Clear voice, and solid connection for data with the one tower with band 17.   

@obtrunco - the 4G alpha tag on the iPhone 7 is just how the phone is interpreting the 3G protocols (HSPA+) as @lizdance40 indicated, and it is a bit misleading. The speeds on the MicroCell have always been limited to around 3.0Mbps download. That is not throttling but rather the limitation that AT&T put on the MicroCell because 3.0Mbps is perfectly sufficient for voice, which is what the MicroCell is primarily intended for. Data should be handled by your WiFi connection so that's why we recommend always leaving WiFi enabled on your phone. We have never had any issues with any of our iPhones (3GS, 5S, 5SE, 7). If you disable WiFi on your phone and then try to use your phone as an internet device from home via the MicroCell, the speeds will definitely suck for the reasons I just mentioned. Voice quality on any of our iPhones has always been excellent and will WiFi enabled, sending/receiving messages, videos, pics, and even FactTiming on the phones that are capable has been trouble-free.

WiFi-C (WiFi Calling) on the iPhone 7and SE is much better, and more reliable than the MicroCell, so if  you don't need the MicroCell for other non-WiFi-C capable phones, then I'd see if that works better for you and just disable the MicroCell (make sure you deactivate it from your account first if you choose to sell it or give it away).